Process for fractionating hydrocarbon oils



Patented Nov. 21, 1939 PROCESS FOR FRAGTIONATING HYDROCARBON OILS Gerritt Willem Nederbragt, Amsterdam, Netherit lands, assignor to Shell Development Company, San Francisco, Calif a corporation of Delaware No Drawing. Application September 27, 1938, Serial No. 231,904. In the Netherlands March This invention relates to a process for the separation of hydrocarbon mixtures, such as mineral oils, particularly gasoline, kerosene, gas oil, lubricating oils, and the like, derived from petroleum, tar oil, shale oil, etc., into fractions which are,

. respectively, more aromatic and less aromatic.

The less aromatic fraction, herein designated as essentially non-aromatic, may be slightly aromatic or substantially non-aromatic in character,

such as a fraction consisting mainly of paraffins or naphthenes, or both. The invention is par,- ticularly useful for the fractionation of substantially wax-free oils, 1'. e., oils which are liquid at about 0 0., wherein it is desired to produce a normally liquid essentially non-aromatic product which includes all or substantially all of the nonaromatic hydrocarbons present in the initial oil subjected to the treatment.

The term essentially non-aromatic is intended herein to denote products, which, while they may contain some aromatics, are less aromatic in character than the initial substantially Wax-free oil being fractionated.

It is known to fractionate mineral oils or fractions thereof into components or groups of components which are relatively more aromatic and lessaromatic in character, respectively, by extraction with a liquid selective solvent for aromatic hydrocarbons, under conditions which cause the formation of two liquid phases or layers, the solvent-rich or extract phase containing the most aromatic hydrocarbons in solution, and the oilrich or raffinate phase containing-the least aromatic hydrocarbons, with a small amount of the solvent. The separations thus obtained are sharper when more stages are employed. Sucha treatment may, for example, be carried out in a number of mixers and settlers, the selective solvent being flowed in countercurrent to the mixture being fractionated or extracted. In view of the fact that a sharp separation cannot generally be effected by employing, only single-stage extraction, it is practically necessary to operate such solvent extraction processes. in a countercurrent manner, which necessitates the use of a complicated apparatus. v

vIt is also known to carry outthe solvent extraction of Wax-containing oil with selective solvents at temperatures causing wax to be solidified and dispersed inthe ramnate phase or at the 8 Claims. 01. 196-13) interface of the extract and raiiinate phases, the V separationof the extract phase being carried out 'so as to form a mixture of liquid raffinate phase and solid wax;-this mixture is then treated to separate the solid wax from the liquid raffinate phase by a suitable method, such as filtration, the final liquid product being derived entirely from the liquid rafiinate phase after the removal of solvent therefrom. Further, it is known to separate certain components or groups of components from the mixture in the solidstate by cooling the hydrocarbon mixture in the presence of a diluent. In this way fractions having a lower melting point than paraffin wax can be solidified and separated from fractions which, at least in the presence of the diluent, having still-lower melting points; paraffin wax, if present in the initial hydrocarbon mix-' ture, is present in the solidified. fraction. Since aromatic hydrocarbons generally crystallize out less readily from asolvent-or mixture of solvents than non-aromatic hydrocarbons, it is possible, when applying this process, to obtain the components or groups of components as a rule in a fairly pure state and often even in a very pure state, at least as longas the process is restricted to the separation of those non-aromatic components which crystallize out most readily. If-

it is desired to separate off the greater part of the non-aromatic components in-the solid state by applying extremely low temperatures, they are often contaminated with aromatics whichv are also solidified.

In accordance with the present invention, it

was found that particularly good results in fractionating such substantially wax-free hydrocarbon mixturesare obtained by chilling the mixture in the presence of a solvent to form three simultaneous, phases, i. e., two liquid phases and a solid phase, separating the liquid extract or solvent-rich phase from the other two, and form- I ing a normally liquid product of lesser aromaticity than the oil in said extract phase containing oil from the-liquid raflinate phase and from the j solid phase;

Briefly, the process comprises the following steps: The initial hydrocarbon mixture is cooled in the presence of a selective solvent (which may be a mixture of solvents) for aromatic hydrocarbons, the cooling being deep enough, e. g. to

about 35 C. to -125 C., to cause a portion of the mixture to become solidified, and the unsolidified portion to form two or more liquid phases. The initial mixture may be completely or partially dissolved in the solvent prior to chilling, or the solvent may be added to the mixture during the cooling step or even afterwards, as described inthe U. S. Patent No. 2,108,629. From one half tothree volumes of solvent for one volume or initial, substantially wax-free oil are normally suitable, although the invention is not restricted to these ratios. The liquid extract phase is then separated from the solid and liquid rafiinate phase at the low temperature by any suitable method.

In the preferred embodiment of the process, the solidified portion, often with a considerable quantity of liquid oil from the ramnate phase adhering to it, is separated from the two liquid phases by any suitable method, preferably filtration, the filter cake being either solid or a filterable pasty mass containing the solidified portion. The two liquid raifinate and extract phases are then separated from one another, as by settling or centrifuging, and the oil'from the raffinate phase is combined with the oil from the filter cake, either in the solid or melted state. The solvent may be removed from the filter cake and from the liquid raffinate phase prior to blending, but it is usually simpler to combine the filter cake with the rafiinate phase directly, warm the resulting mixture to melt solids, and separate the solvent therefrom by distillation or washing with a suitable solvent, such as water or a watermiscible organic washing agent like methyl alcohol which is at least partially immiscible with the oil and substantially completely miscible with the selective solvent; traces of the washing agent remaining in the oil may then be removed by washing with water or by steam distilling.

It is also possible to efiect a single, or direct separation by separating the liquid extract phase from the mixture of the liquid raffinate phase and the solid phase by decantation and removing the solvent from the latter mixtureto produce a liquid product containing the hydrocarbons of the solid and liquid rafiinate phases.

Finally, these methods may be combined by skimming a quiescent mixture of the three phases to remove the solids together with a considerable portion of the liquid raffinate phase and subsequently effecting a more careful separation between the remaining liquid layers, of which the raffinate layer is combined with the materials removed in the skimming step.

The separated crystallized mass according to any of these methods, may be subjected to the usual finishing treatments, such as acid or clay treatment, either alone or together with the oil from the liquid raffinate phase.

By proceeding in accordance with the present process a sharper separation into components or groups of components of a high degree of purity is effected in a simple manner, whilst moreover, at the same temperature, a higher yield is obtained than when applying the process under conditions causing only one solid and one liquid phase to be formed, i. e. without causing demixing of the components that have remained liquid. Further, the separation of the solid and the two or more liquid phases in general seems to be greatly facilitated by the crystals clogging or adhering together with the demixed rafiinate oil to form a thick paste, an effective separation between the solvent or extract phase and the other phases being obtainable by mere decantation or skimming. In fact, to achieve good results with the present process it is generally sufficient to obtain the solid phase together with a large portion of the liquid raflinate phase, this condition being contrary to that required in dewaxing processes wherein the wax cake should be as dry and free from oil as possible. The present process should be distinguished from dewaxing processes in which solid Wax is separated from two liquid phases, and the waxis washed to remove oil adhering thereto. In such processes the separation effected is between wax and oil, the latter containing non-aromatic hydrocarbons, while in the present process the solid and one of the liquid phases are combined to form a combined normally liquid product containing as much as possible of the non-aromatic oil.

When starting with a wax-bearing oil, it is desirable to separate the wax in a preliminary treatment, as illustrated in the example. The same solvent may be employed in such a dewaxing step as in the subsequent low-temperature, three-phase separating step; or, where a mixture of solvents is used in the low temperature step, one of the solvents or a mixture of solvents in a diiferent proportion may be used for dewaxing. This renders the process particularly attractive, since it is not necessary to separate the dewaxing solvent from the dewaxed oil, the desired separations being then achieved merely by successive coolings and phase separations, possibly with the addition of more solvent.

It is preferable to employ solvents which have a sufficient solvent power to dissolve all of the liquid components at temperatures at which the solidification of components begins; otherwise the demixing of the liquid components into two liquid phases would precede or take place simultaneously with incipient solidification, an occurrence which was found to be undesirable. The solvent power of the selective solvent for aromatics can be increased, if necessary, by the addition of solvents with a high solvent power for both the hydrocarbons and the selective solvent, such as toluol, chloroform, ethers like ethyl ether, carbon disulfide, andthe like.

Any selective solvent for aromatics which is liquid at low temperatures or which is liquid at low temperatures under the conditions of the process, i. e., when in contact with the hydrocarbons or diluted with a solvent having a high solvent power as described above, may be employed. Themost suitable selective solvents are esters, suchas methyl formate and ethyl acetate, ketones, such as diethyl ketone and acetone, alcohols, such as methyl-, ethyl-, and isopropyl alcohol, and heterocyclic ring compounds, such as apicoline and'furfural, or mixtures. thereof.

Example. I..A Venezuelan distillate oil having a density of 0.8586

(all densities are d 2 was dewaxed at -15 C. with 200%v. (percent' The filtrate, consisting of the filter oil and washing liquid, was then treated according to aromatic product amounting to 49%w. (calcu lated on the initial oil), having a density of 0.8445 and a viscosity index of 88. The liquid extract (solvent-rich) phase yielded 31%w. of an oil with a density of 0.9165.

Example II.A Venezuelan distillate was de-' Waxed with 240%v. ethyl acetate+60%v. toluol at 15 C. by filtration, the cake being Washed with a mixture of 80%v. ethyl acetate+20%v. toluol, and the washing liquid was added to the filtrate. The wax thus separated amounted to 18%w. and had a density of 0.8053; the oil in the combined filtrate and washing liquid amounted to 82% w. and had a density of 0.8708 and a viscosity index of 65. The latter was then cooled to 50 C., causing a portion to crystallize out and the liquid to separate into liquid rafiinate and extract layers; The liquid extract phase was separated from the mixture of crystallized mass and liquid raflinate phase by decantation. The mixture containing the crystallized material and the raffinate oil (in this particular case the solvent was removed in order to determine the properties of the oil; in practice such removal of the solvent will generally be dispensed with) constituted 44%w. of the initial oil, and had a density of 0.8392; the oil from the extract phase amounted to 38 %w. and had a density of 0.9101.

The said parafiinic mixture was diluted with 320%v. ethyl acetate and again cooled to 50 C. At this temperature a separation was again effected into 38%w. cake (consisting of crystallized mass and liquid rafi'inate phase), having a viscosity index of 99, a pour point of -4 C. and a density of 0.8310, and 6%w. filter oil (derived from the liquid extract phase), having a density of 0.8950.

I claim as my invention:

1. Process for producing a normally liquid,

essentially non-aromatic hydrocarbon product.

comprising the steps of dewaxing a wax-bearing hydrocarbon mixture in the presence of a selective solvent for aromatic hydrocarbons to produce a solution of a substantially wax-free hydrocarbon mixture in said solvent, removing the wax from said solution, cooling said solution to a temperature between about 35 C. and 125 C. sufiiciently low to solidify a portion of the hydrocarbons as a solid phase and form simultaneous liquid raiiinate and extract phases, said solvent being capable of forming said two liquid phases at said low temperature and having a sufficient solvent power to dissolve all liquid hydrocarbons in a single liquid phase at a higher temperature at which at least a portion of the wax-free hydrocarbons are solidified, separating the solid phase from the liquid phases, separating the remaining liquid phases one from the other, combining hydrocarbons in the separated solid phase with hydrocarbons in the separated liquid railinate phase and reliquefying the hydrocarbons essentially non aro'matic hydrocarbon product comprising the steps of dewaxing'a wax-bearing hydro'carbonmixture in the presence of a selective solvent for aromatic hydrocarbons to produce a solution of a substantially wax-free hydrocarbon mixture in said solvent, removing the Wax from said solution, cooling said solution to a temperature between about 35 C; and -125 C. sufficiently low to solidify a portion of the hydrocarbons as a solid phase and form simultaneous liquid rafiinate and extract phases, said solvent being capable of forming said two liquid phases at said low temperature and having a sulficient solvent power to dissolve all liquid hydrocarbons in a single liquid phase at a higher temperature at which at least a portion of the waxfree hydrocarbons are solidified, separating the liquid extract phase from the solid phase and the liquid rafiinate phase and reliquefying the hydrocarbons in the solid phase, to form a normally liquid, essentially non-aromatic product containing hydrocarbons from the solid phase and from the liquid raflinate.

3. The process according to claim 2, in which the liquid extract phase is separated directly from the solid phase and from the liquid rafiinate phase in a single separation.

4. Process for producing a normally liquid, essentially non-aromatic hydrocarbon product comprising the steps of dewaxing a Wax-bearing hydrocarbon mixture to produce a substantially wax-free hydrocarbon mixture, forming a system containing said wax-free hydrocarbon mixture and a selective solvent for aromatic hydrocarbons at a temperature sufiiciently low to solidify a portion of the hydrocarbons as a solid phase and form simultaneous liquid rafiinate and extract phases, separating the liquid extract phase from the solid phase and the liquid rai'linate phase and reliquefying the hydrocarbons in the solid phase to form a normally liquid, essentially non-aromatic product containing hydrocarbons from the solid phase and from the liquid raifinate.

5. Process for producing a normally liquid, essentially non-aromatic hydrocarbon product comprising the steps of cooling a substantially wax-free hydrocarbon mixture and a selective solvent for aromatic hydrocarbons, and mixing said solvent and mixture to produce a cooled system having a temperature sufliciently low to solidify a portion of the hydrocarbons as a solid phase and to form simultaneous liquid rafiinate and extract phases, separating the liquid extract phase from the solid phase and the liquid raflinate phase and reliquefying the hydrocarbons in the solid phase to form a normally liquid, essentially non-aromatic product containing hydrocarbons from the solid phase and from the liquid raflinate.

6. The process according to claim 5, in which the liquid extract phase is separated from the solid phase and liquid rafiinate phase by first separating the solid phase from the'two liquid phases, separating the remaining liquid phases one from the other, and combining hydrocarbons from the separated solid phase with hydrocarbons in the separated liquid rafiinate.

7. The process according to claim 5, in which the liquid extract phase is separated directly comprising the steps of dissolving a substantially wax-free hydrocarbon mixture in a selective solvent for aromatic hydrocarbons, said solvent having a sufficient solvent power to dissolve all liquid hydrocarbons at a temperature at which at least a portion of the Wax-free hydrocarbons are solid and being capable of forming liquid raffinate and extract phases at a lower temperature, cooling said mixture and solvent to said lower temperature between about 35 C. and -125 C, sufficiently low to solidify a portion of the hydrocarbons as a solid phase and. to form simultaneous liquid raffinate and extract phases, separating the liquid extract phase from the solid phase and the liquid raffinate phase and reliquefying the hydrocarbons in the solid phase to form a normally liquid essentially non-aromatic product containing hydrocarbons from the solid phase and from the liquid raflinate.

GERRIT WILLEM NEDERBRAGT. 

